Linear Motion Peening

ABSTRACT

This invention utilizes a linear motor to impact peening media. It has three major applications: (1) deep compression low surface work peening, (2) Almen strip arc height testing and (3) manual peening. This process differs from existing processes in that impacts are controlled in position, velocity and mass. The indentor tip may have single or multiple indentors. 
     In its deep peening/low surface work this invention competes with processes such as Roller Burnishing, Low Plasticity Burnishing and Laser Peening. 
     The Almen strip testing application fills a void in shot peening quality control. There are examples of Almen strips whose arc height behavior differed side to side. Others have differed between lots. Recent peening production lines have been shut down by incorrect arc heights. 
     This invention is an alternative to manual peening processes such as Flapper peening and hand held nozzle peening.

BACKGROUND INFORMATION

The linear motors used in this invention are tubular devices containing motor windings and rare earth magnets. The motion produced is linear. Linear motors are commonly used in industrial applications where rapid movement and strict control of position, velocity and force is required. Linear motion is produced without the use of intermediary mechanical devices such as gearboxes and belts and control is by a microprocessor based servo drives. Feedback is internal to the motor.

Almen strips as specified in SAE J442 are accepted industry-wide for measuring peening intensity. They come in three thicknesses, A at 0.051 inch, C at 0.094 inch, and N 0.031 inch, all ¾ inch in width and 3 inches in length. Made from 1070 steel, the specified strip hardness is Rockwell C 44-50, or 45-48. The Almen gage specified in SAE J442 measures the arc height of the center 1¼ inches of the 3 inch length. It is believed that the A strip thickness was chosen so that the measured arc height would be the same as the compressive depth of a 1070 steel component peened under the same conditions.

Many production peening processes require intensities to be maintained to very close tolerances. Other peening processes may allow wider intensity ranges to accommodate locations peened at different impingement angles (intensity varies with the sine of that angle). Such processes may have intensities (at different part locations) that near both upper and lower limits and therefore also require precise intensity control. Intensity deviations caused by Almen strip arc height errors can severely affect part quality and production schedules. Unfortunately, such deviations have been experienced in the past with Almen strips that met all specification requirements—the relevant ones being material chemistry, thickness and hardness. A production shop has no way of proving deviant arc height behavior. Producers of Almen strips have no precise way of qualifying their strips to an arc height standard to prevent this deviation.

A limited search for prior art in indentor peening and deep low surface cold work peening produced only a few patents, but none directly competing. Representative patents include: U.S. Pat. No. 6,742,377 “Passive-adaptive indentor for stress wave cold working”, U.S. Pat. No. 5,826,453 “Burnishing method and apparatus for providing a layer of compressive residual stress in the surface of a workpiece” and U.S. Pat. No. 4,401,477 “Laser shock processing. None employs a linear motor. An indentor peening process in U.S. Pat. No. 5,771,729 also does not employ a linear motor.

EXPLANATION OF DRAWINGS

FIG. 1 is a sectional view of a linear motor showing the slider winding (3), stator winding (2), sensors and electronics (1) and the indentor tip mounting location (4).

FIG. 2 shows several indentor tips, three (5,6,7) with small to large ball tips and one with multiple balls (8).

FIG. 3 shows a simulated 90 degree impact arrangement design for holes. The primary indentor (9) impacts the secondary indentor (11) which in turn impacts a ring of balls (12). The tapered plug (13) forces the ring balls against the hole (10).

FIG. 4 shows an Almen strip test rig. The linear motor slider (14) with indentor (15) impacts the Almen strip (16). Coordinated motions are provided by longitudinal indexing motor (17) and transverse motor (18).

FIG. 5A a similar setup for a flat fatigue specimen (19) with longitudinal (20) and transverse (21) motors.

FIG. 5B shows cylindrical fatigue test specimen (22) mounted in cradle (23) with longitudinal motor (25) and rotation motor (24).

FIG. 6 shows an indentor (26) attached to a flex shaft (27) and sheath (28).

FIG. 7 shows a manual setup with indentor (29) handle (30) and linear motor (31). 

What is claimed is:
 1. A method of peening in which surface compression producing dimples are created by an indentor driven by a position, velocity and mass controlled linear motor.
 2. A method of linear motor peening in which the impacts are synchronized with the lateral motions of the indentor.
 3. A method of linear motor peening in which the impact face of the indentor may have single or multiple impact shapes.
 4. The method of linear motor peening in which the linear motor shaft is directly connected to the indentor.
 5. The method of linear motor peening in which the linear motor shaft is connected to the indentor by an arrangement which translates the motion by 90 degrees to peen holes or other limited access areas.
 6. The method of linear motor peening in which the linear motor shaft is connected to the indentor by angled impact of a secondary impactor which translates the motion by 90 or less degrees to peen holes or other limited access areas.
 7. The method of linear motor peening in which the linear motor shaft is connected to the indentor by a flexible shaft which translates the motion off angle to peen limited access areas.
 8. The method of linear motor peening in which the linear motor shaft is connected to the indentor by a hydraulic line which translates the motion off angle to peen limited access areas.
 9. The method of linear motor peening in which a method of testing and qualifying Almen strips for arc height performance under conditions demonstrated to exhibit anomalies in arc height behavior in which the indentor is horizontally and longitudinally motion programmed to achieve dimple coverage on the Almen strip.
 10. A method of linear motor peening fatigue test specimens in which the indentor is horizontally and longitudinally motion programmed to achieve dimple coverage on the specimen.
 11. A method of linear motor “automated” peening in which the linear motor equipped with an indentor is mounted on a robot whose positions and motions are integrated with the indentor impact motions.
 12. A method of linear motor manual peening in which the linear motor equipped with an indentor which is hand manipulated.
 13. A method of linear motor manual peening in which the linear motor is fixtured and the indentor is mounted on a flex shaft which is hand manipulated. 